Photocell arc timer



April 18, 1967 w. F. ICELAND PHOTOCELL ARC TIMER Filed Sept. 4, 1963 D N M R E mxfi m M w t A F. a w V M 4M1 1 N W M mm am 3 U m wt h m V. 5 w Ur cfi 1W. 5:28. New [39G ERR HQ \3 4 \4 93 Q mm 555% UP United States Patent 3,315,126 PHUTUCELL ARC TIMER William F. Iceland, Los Angeles, Calif., assignor to Air Reduction Company, Incorporated, New York, N.Y., a corporation of New York Filed Sept. 4, 1963, Ser. No. 306,575 1 Claim. (Cl. 315-151) This invention relates to means for timing the duration of an operation involving the use of an electric arc, and more particularly to means utilizing radiant energy from the arc to actuate the interval duration timing device.

In accordance with the invention, I impress electrical voltage pulses upon a control circuit which includes a photocell that is exposed to radiant energy from the electric arc whenever the arc is in operation. The control circuit also includes an impedance element, for example a potentiometer from which a train of pulses is taken olf and impressed upon a pulse or cycle counter of a type known to the art. In the absence of radiant energy from the arc, the photocell has a very high impedance so that as a result there is substantially no current passed through the potentiometer and no pulses are impressed upon the cycle counter. When the photocell is being irradiated, however, a train of pulses is impressed upon the cycle counter. The cycle counter may be set to time out any desired time interval and to initiate any desired switching operation at the end of the timed interval.

An advantage of the invention is the absence of any wiring or other tangible connection between the arc circuit and the photocell, an advantage not shared by other types of devices for sensing or monitoring the existence of actual arc operation, such as means for sensing the voltage between the arc electrodes.

Other features, objects and advantages will appear from the following more detailed description of an illustrative embodiment of the invention, which will now be given in conjunction with the accompanying drawings.

In the drawings,

FIGURE 1 is a block schematic diagram showing an embodiment of the invention; and

FIGURE 2 is a graph showing typical wave patterns to be found in a system according to the invention.

Referring to the drawings, FIGURE 1 shows a photocell positioned so as to be directly exposed to radiation from an electric arc, which latter is shown schematically at 12 between an arc Welding or cutting elec trode 14 and a workpiece 16. The path of the radiation is shown schematically by broken lines 18. The photocell 10 is serially connected to the output side of a rectifier together with a potentiometer 22 and a protective or current-limiting resistor 24. The rectifier 20 is energized by an alternating current source 26 through a voltage step-up transformer 28.

The are 12 is supplied with source 30 under the control solenoid 32 for opening and closing a contactor 34 in serial relationship between the are 12 and the source 30. The solenoid 32 is arranged to be energized by the alternating current source through a rectifier36 under the joint control of a starting switch 38 and a normally closed contact 40 ofa relay 42. The relay 42 is in turn controlled by a cycle counter 44 which is energized by pulses led olf from the potentiometer 22 when the are 12 is in operation, as will be explained below.

In the operation of the system of FIGURE 1, closure of the starting switch 38 causes the alternating current source 26 and rectifier 36 to energize the solenoid 32 through the contact 49 of the relay 42. The operation of the solenoid 32 causes the contactor 34 to elfect the connection of the are power source 30 to the electrode power from an are power of a switch shown as a 14 and workpait 16 to actuate the are 12. As soon as the are 12 is established, radiation from the arc, of a form to which the photocell 10 is sensitive, renders the photocell electrically conductive, thereby passing current pulses from the rectifier 20 through the potentiometer 22 and resistor 24. A train of pulses, at the pulse rate of the rectifier 20 is thus impressed upon the input of the cycle counter 44. The cycle counter 44 is of conventional type which may be set to count any desired number of individual pulses and to perform a switching operation upon completion of the count. As shown in FIGURE 1, the cycle counter 44 has its output connected to the re lay 42, so that when the desired count is completed the relay 42 operates to open the contact 40, thereby de-energizing the solenoid 32 and breaking the welding circuit through the contactor 34. The duration of the welding operation is thus timed out by the operation of the cycle counter 44. Additional switching means (not shown) may be provided in conventional manner known to those skilled in the art to restore the cycle counter 44, relay 42 and starting circuit to normal after the timing out of a welding operation as just described in order to condition the system for starting and timing another welding operation.

FIGURE 2 illustrates graphically the formation of pulses in the circuit of the potentiometer 22, when the rectifier 20 is a full wave rectifier, and during a time interval when the photocell 10 is being irradiated by suitable radiation from the arc 12. In the absence of a voltage across its electrodes, the photocell 10 is substantially non-conductive of electric current. The photocell does not become conductive until the voltage across its electrodes has risen to a certain threshold value, whereupon it suddenly becomes conductive and remains so until the voltage across its electrodes is reduced to zero. The voltage wave developed by the rectifier 20 is shown in FIGURE 2 as a succession of half-wave sinusoidal pulses 50. The resulting current through the potentiometer 22 is shown by the succession of pulses 52 which constitute a pulse train with a pulse rate equal to twice the frequency of the alternating current source 26. The pulses 52 are of a form suitable for actuating a cycle counter of the type contemplated for use as cycle counter 44 in FIGURE 1.

It will be evident that the rectifier Zil functions primarily as a generator of a train of pulses, which pulses are substantially sinusoidal. The train of pulses reaching the cycle counter has the same repetition rate as the pulse train generated by the rectifier but the pulse shape is modified by the action of the photocell. The resulting pulses, however, are suitable for properly actuating the cycle counter. It will be appreciated that the rectifier 20 may be either a full-wave or a half-wave rectifier. As a full-wave rectifier gives twice as many pulses in a given interval it is usually preferred over a half-wave rectifier. Moreover, in general any suitable generator of a pulse train which will actuate the cycle counter may be substituted for the rectifier.

The invention may be used with substantially any known type of electric arc welding equipment, including both alternating current arcs and direct current arcs, and with or without a mantle of shielding gas surrounding and protecting the region of the arc, as long as the photocell is actually exposed to radiation from the are when the arc is in operation. The photocell may be of any suitable type. One that has been used successfully is a Thomas Edison ultraviolet detector tube which is readily obtainable on the market. A suitable cycle counter for pulses occurring at the rate of, for example pulses per second, is known as an Erie 320 Counter. A suitable source for operating the photocell and cycle counter as well as the associated relays and solenoids is a 115 volt, 60 cycle per second power line. A suitable peak output voltage for the full wave rectifier 20 is 650 volts for operating the Thomas Edison detector tube.

While the receptor of the radiant energy shown herein has been termed a photocell, it will be evident that this is intended as a generic term to include any suitable device which changes its internal electrical character upon being irradiated by radiant energy.

It will be understood that any suitable source of power may be used for operating the solenoid 32 in place of the power supplied from the alternating current source 26 through the rectifier 36 in FIGURE 1. It will also be understood that the devices other than electric arcs may be timed provided only that the device in question while in operation emits radiation of a type to which the photocell or other receptor is sensitive.

While illustrative forms of apparatus and methods in accordance with the invention have been described and shown herein, it will be understood that numerous changes may be made without departing from the general principles and scope of the invention.

I claim:

Apparatus for the working of metals by the direct application thereto of an electric are sustained for a precise predetermined length of time between an electrode and the metal to be worked comprising a source of power for said are, means for connecting said source of power in a circuit with said electrode and said metal to be worked to thereby enable said source of power to support said arc,

timing means for timing a precise predetermined length of time, said timing means comprising a source of a train of electrical pulses regularly spaced in time and a pulse counter, said source of a train of electrical pulses operating continuously independently of the operation of said are and the time interval between pulses of said train being independent of the intensity of the radiant energy of said arc, photoelectric means responsive to radiation from said are to render said timing means operative upon initiation of said are and means responsive to the action of said timing means at the expiration of said predetermined time to interrupt the circuit connecting said source of power with said electrode and said metal to be worked to thereby interrupt said are after the arc has been sustained for said predetermined time.

References Cited by the Examiner UNITED STATES PATENTS 1,892,017 12/1932 Stansbury et al 32468 2,031,288 2/1936 Tripp 2l9l35 2,208,386 8/1940 Null 315-151 2,386,320 10/1945 Kott 315151 2,491,428 12/ 1949 Tellier 3 153 60 2,524,100 10/1950 Dauvillier et al 315-101 DAVID J. GALVIN, Primary Examiner.

WALTER L. CARLSON, M. I. LYNCH,

Assistant Examiners. 

